A. Field of the Invention
The present invention relates generally to a magnetic recording medium and in particular, to a magnetic recording medium for use in external storage devices of computers or the like.
B. Description of the Related Art
Various types of lubricants for magnetic recording media, in particular for magnetic disks, have been developed for the purpose of reducing a frictional force generated between a protective layer and a magnetic head, and improving durability and reliability.
In order to improve lubrication performance of a surface layer of a magnetic recording medium, a perfluoropolyether lubricant having a polar end group such as a hydroxyl group or a cyclic triphosphazene end group in the molecule, for example, has conventionally been applied on a protective layer of diamond like carbon (DLC). For example, according to Japanese Unexamined Patent Application Publication No. 2001-006155 a mixture of various types of perfluoropolyether lubricant containing various polar end groups is applied.
In order to achieve a planar recording density over 1 Tbits/in2 in a magnetic recording medium, particle size of the magnetic layer needs to be decreased to reduce noise. An excessively small particle size, however, raises a problem that magnetic signals recorded in the magnetic layer disappear due to thermal demagnetization. Consequently, high density recording requires use of a magnetic layer that exhibits high thermal stability and high coercivity.
Accordingly, Japanese Unexamined Patent Application Publication Nos. 2003-045004 and 2006-012249 have proposed methods in which laser light is irradiated on recording regions of a magnetic recording medium having a recording layer with high coercivity to heat and decrease the coercivity, and a magnetic field is applied to the regions with the decreased coercivity using a magnetic head corresponding to the information to be recorded. This recording method is called thermally assisted magnetic recording.
In the thermally assisted magnetic recording process, a recording layer is heated up to a temperature of about 150° C. by the irradiation of laser light on the recording plane. As a result, the lubricant is exposed to a high temperature due to thermal conduction from the recording layer.
Conventionally used lubricants, however, are not suitable for use in a high temperature environment such as occurs in thermally assisted magnetic recording. Thus, there is a concern about decrease of lubricant due to volatilization in the high temperature environment.
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.